text: The first rain gardens were created to mimic the natural water retention areas that developed before urbanization occurred. The rain gardens for residential use were developed in 1990 in Prince Georges County, Maryland, when Dick Brinker, a developer building a new housing subdivision had the idea to replace the traditional best management practices (BMP) pond with a bioretention area. He approached Larry Coffman, an environmental engineer and the countys Associate Director for Programs and Planning in the Department of Environmental Resources, with the idea. The result was the extensive use of rain gardens in Somerset, a residential subdivision which has a  rain garden on each house's property. This system proved to be highly cost-effective. Instead of a system of curbs, sidewalks, and gutters, which would have cost nearly $400,000, the planted drainage swales cost $100,000 to install. This was also much more cost effective than building BMP ponds that could handle 2-, 10-, and 100-year storm events. Flow monitoring done in later years showed that the rain gardens have resulted in a 75–80% reduction in stormwater runoff during a regular rainfall event.
  Some de facto rain gardens predate their recognition by professionals as a significant LID (Low Impact Development) tool. Any shallow garden depression implemented to capture and filter rain water within the garden so as to avoid draining water offsite is at conception a rain garden—particularly if vegetation is planted and maintained with recognition of its role in this function. Vegetated roadside swales, now promoted as “bioswales”, remain the conventional runoff drainage system in many parts of the world from long before extensive networks of concrete sewers became the conventional engineering practice in the industrialized world. What is new about such technology is the emerging rigor of increasingly quantitative understanding of how such tools may make sustainable development possible. This is as true for developed communities retrofitting bioretention into existing stormwater management infrastructure as it is for developing communities seeking a faster and more sustainable development path.